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Laser-induced graphene (LIG) on paper substrates is a desirable material for single-use point-of-care sensing with its high-quality electrical properties, low fabrication cost, and ease of disposal. While a prior study has shown how the repeated lasing of substrates enables the synthesis of high-quality porous graphitic films, however, the process-property correlation of lasing process on the surface microstructure and electrochemical behavior, including charge-transfer kinetics, is missing. The current study presents a systematic in-depth study on LIG synthesis to elucidate the complex relationship between the surface microstructure and the resulting electroanalytical properties. The observed improvements were then applied to develop high-quality LIG-based electrochemical biosensors for uric acid detection. We show that the optimal paper LIG produced via a dual pass (defocused followed by focused lasing) produces high-quality graphene in terms of crystallinity, sp 2 content, and electrochemical surface area. The highest quality LIG electrodes achieved a high rate constant k 0 of 1.5 × 10 -2 cm s -1 and a significant reduction in charge-transfer resistance (818 Ω compared with 1320 Ω for a commercial glassy carbon electrode). By employing square wave anodic stripping voltammetry and chronoamperometry on a disposable two-electrode paper LIG-based device, the improved charge-transfer kinetics led to enhanced performance for sensing of uric acid with a sensitivity of 24.35 ± 1.55 μA μM -1 and a limit of detection of 41 nM. This study shows how high-quality, sensitive LIG electrodes can be integrated into electrochemical paper analytical devices.

This paper describes the development and characterisation of a novel, electrical impedance spectroscopy-based (EIS) immunosensor array for point-of-care applications. EIS is a highly sensitive, label-free, real time technique suitable for single use, point-of-care cardiac marker detection devices. However, the underlying source of the observed change in EIS immunoassay response has not been well characterised or understood. A full understanding of the relationship between target binding and impedance response would significantly advance biosensor design and most probably increase detection limit sensitivity. The development of micro-/nano- structured electrodes for multi-frequency EIS procedure propose substantial benefits over classical macro-structured systems.Countless manipulations of electrode features and inter-electrode spacing will enhance the electrode surface area, increase the charge-transfer resistance and reduce the double-layer capacitance. These in turn give rise to improved signal-to-noise ratios, therefore affording greater sensitivity, lower detection limits and faster detection times.The sensor sensitivity range was within that required for human myoglobin determination, following acute myocardial infarction (heart attack). Real-time MyAb-MyAg interaction monitoring, permitted the determination of the binding events in less than one minute.

A comparative study into two novel and diverse schemes designed to improve immobilization of biomolecules for biosensing purposes is presented. In the first method a silicon rich matrix is created using PECVD. The second method involves creating nano-patterns on the sensor surface to create a large number of surface discontinuities to which the proteins will bind preferentially. The basic theory of SPR is provided to show the importance of the surface sensitive nature of this optical transduction technique. The present work suggests that both may prove both for SPR and other biosensing applications. Of the two schemes proposed, the results for nano-patterning seem to suggest that it is promoting better surface attachment of biomolecules. The results of SPR and AFM studies are presented that have shown that each of these schemes promotes improved binding of various proteins.

Miniaturised point-of-care cardiac marker sensors are being developed, based on impedimetric sensing of cardiac enzyme capture by an antibody layer immobilised on a planar gold electrode sensor. Gold/Ti-on-glass substrates have been used, in a 2 electrode configuration, with antibodies immobilised on the working electrode. Microfluidic structures have been fabricated by a CO2 laser, in 25 mum thick pressure sensitive adhesive (PSA), on a PMMA lid, and the structure bonded on top of the planar sensor. Microfluidic blood/serum delivery has been investigated using a visualisation dye. Some flow problems are observed if the sensor is exposed to air for several days, suggesting that flow channel nanopillars and hermetic encapsulation may be required to guarantee flow properties in commercially produced modules. Work is ongoing to characterise the impedimetric signal changes for myoglobin capture by antimyoglobin, using these sensors. Fifty micron thick PSA, incorporating a robust spacer layer, will be used to give better definition of channel walls.

With the development of critical areas of interdisciplinary research, scientists will lead to an enhanced understanding and control of the key processing stages involved in the design and manufacture of sensor-and electrode-based micro-devices such as micro total analysis systems (muTAS), bio-chips, bio-arrays and DNA sensors. It is anticipated that this fundamental work will lead to tangible technology transfer in the areas of blood analysis, cardiac enzyme detectors, liver and renal function, infectious diseases, gene disorders, etc. These will obviously have major benefits to healthcare delivery. The development of miniaturised, integrated sensor/electrode-based devices are revolutionising both the delivery of health care. In this paper, some of the most exciting research themes in these areas are identified, as well as novel underpinning fabrication technologies and transduction principles, which should make future advances possible.